1. Field of the Invention
The present invention relates to a mechanical seal having an external casing, which is, for example, used as a shaft seal device in a cooling water pump for an automobile engine.
2. Description of the Related Art
External-casing type mechanical seals are known, as illustrated in FIG. 1 as a type of mechanical seal (see Japanese Utility Model Publication H1-18931 and U.S. Pat. Nos. 5676382, 5199719, 4779876, and 4451049) Such a mechanical seal roughly consists of an inner circumferential casing which is secured to, and rotates with, the shaft of a drive mechanism, for example, an automobile engine cooling water pump, and an outer circumferential casing which is secured to a pump housing. A mating ring 1 as a sliding [mating] member, which rotates with the shaft, is installed in the inner circumferential casing; and the inner circumferential and the back face sides of the mating ring 1 are press fit via a cup gasket 2 into a roughly U-shaped cross-sectional end 3a of sleeve 3.
In the outer circumferential casing, a seal ring 4 which slides against the mating ring 1 and a bellows 5 which is used for biasing the seal ring 4 in an axial direction are arranged adjacently to each other and are fitted in a roughly U-shaped cross sectional cartridge 6. Bellows 5 ends 5a and 5b are both biased in the axial direction by a coil spring 8 through a spring holder 7 and also are securely adhered to the seal ring 4 and the cartridge 6.
In the aforementioned inner circumferential casing, the mating ring 1 is press fit into the roughly U-shaped cross-sectional end 3a of the sleeve 3 via a cup gasket 2 while in the outer circumferential casing, the seal ring 4 is fitted into the cartridge 6 via bellows 5, spring holder 7 and bellows 5; and then sleeve 3 inner casing portion 3b is inserted in the inner side of the inner casing 6b of the cartridge 6; then the tip 3c of the sleeve 3 inner casing 3b portion is flared, whereby a mechanical seal is integrated. Said mechanical seal integrated in such a manner is press fit using a mounting jig , for example, around a pump shaft and into the housing.
The sliding face 4a of the seal ring 4 is pressed by the biasing forces from the bellows 5 and coil spring 8 which are exerted in the compressed state in the axial direction against the mating ring 1 so that an appropriate face pressure is provided thereto.
However, the type of mechanical seal illustrated in FIG. 1 is deficient in that in attempting to conform to the recently accelerated downsizing trend, for example, in cooling water pumps, on which the mechanical seals are mounted, it is difficult to reduce the size of the coil spring 8 in the axial direction without increasing its diameter; this is because the coil spring 8 which extends in an axial direction is fitted into the cartridge 6, and bellows 5 ends, 5a and 5b, are both held within the cartridge 6, so that the mechanical seal does not structurally permit its substantial size reduction or downsizing in an axial direction, thereby hindering the effort to downsize a pump.
Another deficiency is that in the mechanical seal illustrated in FIG. 1, the face pressure on the sliding face 4a of the seal ring 4 against the mating ring 1 is produced by the biasing force of coil spring 8 coupled with the biasing force of bellows 5, where the proportion of the biasing force from the bellows 5 is relatively large with respect to the entire biasing force, which, coupled with the inevitable variations in the biasing force depending upon the parts manufacture and mounting precision, makes these adverse effects on seal performance unavoidable.
The present invention is aimed at downsizing and providing a mechanical seal with minimal variations in load at the sliding surface.